Calm down. He is just overly picky. Yes there are checkered patterns, that is because the browser prioritises to render your view right away, instead of waiting for most of the page to be rendered. Of course it will pre-render the remaining page as soon as possible, but it can't always be instant. Also, sometimes a cached rendering will be swapped out or invalidated, e.g. when you zoom in. If you scroll really fast, the browser won't have a cache yet and show you the pattern instead. However, just waiting for a second will allow it to catch up again.

Perhaps the iPhone 3GS browser is better at avoiding this, but then the iPhone browser doesn't offer you full desktop-capability rendering at near full desktop resolution.

Scrolling speed in general can be described as smooth, maybe not "silky smooth". We are talking about differences like comparing 25 FPS to 30 FPS. Calling it "jerky" would be beyond unreasonable.

It is true that playing media files in the background noticeably reduces smoothness of panning animations (we are also talking about a very minor stuttering here though, that most people will probably be hard pressed to notice). I would imagine that it would depend on the type of media being played, as some formats are more expensive to decode than others, but I haven't done any testing with this yet. This doesn't really effect the usability of the device at all, but it does slightly effect its aesthetic appeal (if you are able to notice it).

And finally, if you run too many tasks, things will start to get a little jerky of course. It doesn't mean unusable though, and everyone will have their own level of tolerance which decides how many tasks they are comfortable running at the same time. For me it is usually around six tasks, unless I have very good reason to run more than that (which is very rarely the case), as closing and opening tasks is quick and painless.

Frankly, I think it is a bit silly to pretend to speak for the "average user" at this time, when the device is actually available. Why don't we let the average user decide for themselves? If you are keeping and even enjoying the device, I find it fairly disingenuous to use catchy headlines like "yes, it sucks", which needlessly make potential users nervous.